1. Field of the Invention
The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery having a cap plate, an insulation plate, and a terminal plate shaped to prevent the terminal plate from rotating when assembling a cap assembly.
2. Description of the Prior Art
As portable wireless appliances including video cameras, portable telephones, and portable computers tend to have a reduced weight while incorporating more functions, much research is conducted on secondary batteries which are used as the power source for driving the appliances. Secondary batteries include nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, and lithium secondary batteries. Among them, lithium secondary batteries are rechargeable and can be made in a compact size with a large capacity. In addition, lithium secondary batteries have a high operating voltage and a high energy density per unit weight. Therefore, lithium secondary batteries are widely used in the cutting-edge electronic appliance field.
FIG. 1 is an exploded perspective view showing a conventional lithium secondary battery. The lithium ion secondary battery is formed by placing an electrode assembly 112 including positive and negative electrode plates 113 and 115 and a separator 114 into a can 110 together with an electrolyte and sealing the top opening 110a of the can 110 with a cap assembly 120.
The cap assembly 120 includes a cap plate 140, an insulation plate 150, a terminal plate 160, and an electrode terminal 130. The cap assembly 120 is coupled to the top opening 110a of the can while being coupled to a separate insulation case 170 to seal the can 110.
The cap plate 140 may be made of a metal plate and may have a size and a shape corresponding to the top opening 110a of the can 110. The cap plate 140 has a first terminal through-hole 141 formed at the center thereof with a predetermined size into which the electrode terminal 130 is inserted. A gasket tube 146 is coupled to the outer surface of the electrode terminal 130 and inserted together with the electrode terminal 130 into the first terminal through-hole 141. The gasket tube 146 provides insulation between the electrode terminal 130 and the cap plate 140. The cap plate 140 has an electrolyte injection hole 142 formed on a side thereof with a predetermined size. After the cap assembly 120 is assembled to the top opening 110a of the can 110, an electrolyte is injected via the electrolyte injection hole 142, and the electrolyte injection hole is then sealed by a cap 143.
The electrode terminal 130 is coupled to a negative electrode tab 117 of the negative electrode plate 115 or to a positive electrode tab 116 of the positive electrode plate 113 and may act as a negative or positive electrode terminal.
The insulation plate 150 is made of an insulation material, such as a gasket, and is coupled to the lower surface of the cap plate 140. The insulation plate 150 has a second terminal through-hole 151 formed in a position corresponding to the first terminal through-hole 141 of the cap plate 140 so that the electrode terminal 130 may be inserted therein. The insulation plate 150 has a seating groove 152 formed on the lower surface thereof with a size corresponding to that of the terminal plate 160 so that the terminal plate 160 may be seated thereon.
The terminal plate 160 may be made of Ni metal or an alloy thereof and may be coupled to the lower surface of the insulation plate 150. The terminal plate 160 has a third terminal through-hole 161 formed in a position corresponding to that of the first terminal through-hole 141 of the cap plate 140 so that the electrode terminal 130 can be inserted therein. As the electrode terminal 130 is coupled to the terminal plate 160 via the first terminal through-hole 141 of the cap plate 140 while being insulated by the gasket tube 146, the terminal plate 160 is electrically connected to the electrode terminal 130 while being electrically insulated from the cap plate 140.
When the electrode terminal 130 is coupled to the cap plate 140, insulation plate 150, and terminal plate 160, a predetermined force is applied to the electrode terminal 130 while rotating it so that it is inserted into the first terminal through-hole 141 of the cap plate 140. After passing through the first terminal through-hole 141, the electrode terminal 130 passes through the second and third terminal through-holes 151 and 161 formed on the insulation plate 150 and terminal plate 160, respectively, which are coupled to the lower surface of the cap plate 140. The inner diameter of the second terminal through-hole 151 formed on the insulation plate 150 is equal to or slightly larger than the outer diameter of the electrode terminal 130 insertable therein, so that the outer surface of the electrode terminal 130 is forced against it during insertion. As a result, the insulation plate 150 and terminal plate 160 may rotate about the first terminal through-hole 141 of the cap plate 140 in such a direction that they are uncoupled when the electrode terminal 130 is inserted therein. Particularly, the inner diameter of the third terminal through-hole 161 formed on the terminal plate 160 is slightly larger than the outer diameter of the electrode terminal 130 and the terminal plate 160 is likely to rotate when the electrode terminal 130 is coupled thereto.
In order to couple the assembled cap assembly 120 to the insulation case 170, the insulation plate 150 and terminal plate 160 must be again rotated about the electrode terminal 130 in the opposite direction so that they are arranged in the same direction as the cap plate 140. Such additional work lengthens the process time.
In addition, the terminal plate 160 may partially deform when rotated in the opposite direction because it is made of a thin metal plate.
Accordingly, there is a need for a lithium ion secondary battery having a cap plate, an insulation plate, and the terminal plate shaped to prevent a terminal plate from rotating when assembling a cap assembly.